Magnetic recording material

ABSTRACT

A thermally stable magnetic recording material comprising A. A SUPPORT AND B. A MAGNETIC LAYER, SAID MAGNETIC LAYER BEING COMPOSED OF A FINELY DIVIDED POWDER OF FERROMAGNETIC MATERIAL, WHICH IS DISPERSED IN A BINDER OF A POLYAMIDE IMIDE RESIN.

United States. Patent U91 Akashi et a1.

MAGNETIC RECORDING MATERIAL Inventors: GoroAkashi; Yasuyuki Yamada,

both of Odawara, Japan Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan Filed: Oct. 5, 197] App]. No.: 186,788

Foreign Application Priority Data Oct. 5, 1970 Japan....' 45-87412 US. Cl 117/235, 117/237, 117/240, 117/161 P, 252/6254 Int. Cl. H0lf 10/02 Field of Search 1 17/235-240,

References Cited UNITED STATES PATENTS 6/1968 Se'nkpiel 81 a1. 117/235 111] 3, 21,025 [4 June 28, 1974 3,458,480 7/1969 Schmidt et a] 117/232 X 3,472,815 10/1969 Juveland 1 17/232 X 3,523,824 8/1970 Powers et 'al. 117/235 X 3,551,202 12/1970 Wright et a1... 117/240 X 3,554,984 l/19 7l George 117/161 X 3,630,772 12/1971 Seidel 117/235 Primary Examiner-William D. Martin Assistant Examiner-Bernard D. Pianalto Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak 1 Claim, No Drawings -prising a polyethylene terephthalate support and the 7 used. can withstand temperatures of 90C. atthe highimide resins are prepared as follows:

- .TIlSYPII'iliEliQF.AMQQQA!P99045 7' BACKGROUND OF THE INVENTION g i i I Q I 1. Field of the Invention v I g This invention relates to a magnetic recordingmaterial, and specifically, to a binder component for. use in H000 a magnetic layer of a magnetic recording material. 0

t 2. Description of the Prior Art Conventional magnetic recording materials are produced by coating a substrate of plastic film, such as polyethylene terephthalate, cellulose diacetate, celluamples of the synthetic resin include a vinyl chloride/- vinyl acetate copolymer, poly (bu'tyl acrylate), nitrocel- I lulose, cellulose propionate, cellulose acetate butyrate, There-has been eported a methodfor producing lose triacetate or polyvinyl chloride with a dispersion of a finely divided powder'of ferromagneticmaterial-in'a ethyl Cellulose, a p lyvinyl acetate, styrene/butadiene :polyamideimides by synthesizing tetracarboxylicanhy' [1 solution of a synthetic resin, and drying the coating. Ex- A copolymer, vinyl fluoride resin, a vinylidene chloride 0 fdrides o q a i y y tfimel'mic i S s I copolynier, a butadiene/acrylonitrile'copolymer, chloand polymerizing them 'Wlth dlamlnesschematlcallya I rinated polypropylene, polyvinyl butyral, a chlorinatedf i wfl m vinyl chloride resin, a vinyl-acetate/ethylene copolyo mer, phenol resins, epoxy resins, polyamide resins, polyurethane resins, polyester resins, polyether resins, melamine formaldehyde resins, urea formaldehyde res- I ins, alkyd resins, acrylic resins, silicon resins, ormodified products of these. These resins are used either, alone or in combination of two or'more. v i Q These conventional magnetic recording materials are inferior in thermal stability, and magnetic tapes comabove-mentioned binder, which are now generally 0 c'fllcoon est. in recent years, it has been required to performl magnetic recording at high temperatures in space exploitation or industrial metrology, and the development There has also been found a method for producing ofa magnetic recording media having high'thermal stapolyamide imides by synthesizing aromatic diamines bility has been demanded. I cOnIainlng amide linkages, and reacting the resulting Y a diamine derivatives with pyromellitic anhydride in ac- SUMMARY OF THE PRESENT INVENTION] ggrdance with the following reaction equation Accordingly, 1t s an ob ectof the present invention 010C ocl HN NH, V 4

to provide magnetic recording materials, which can rea t +2 tain the physical properties required of .a magnetic rea cording medium, at a temperature above. 200C, and V I t i v for short periods of use, at a temperature above 400C. isophthnloyl chloride m-phanylanadiamlno According to the present invention, there isprovided j r I a magnetic recording material comprising a substrate Hm NHCO 410m; m1, E fi 3? and a magnetic layer of a finely divided ferromagnetic a material dispersed in a binder, wherein a polyamide .r

{an NHCO DETAILED presentation or THE t vEN'noN 7 The polyamide imide resin used as t-he'binderv in the a present invention is a polymer of a structure in which an amide group is introduced into the main chain of the polyimide. Many varieties of polyamide imide resins are commercially available, and can be optionally utilized in the present invention. Generally, the polyamide.

Polyamide imide resins of the following structures are also known:

CONE

OONH

These known ferromagnetic fine powders or supports A are not particularly limited for the present invention. @The work of the inventors of the present application led to the confirmation that even when a support lof considerably inferior thermal stability is used, the use of the specific polyamide imide resin as a binder can provide magnetic recording materials of considerably improved thermal stability.

; The following Examples will further illustrate the present invention, but are not intended to limit the lscope thereof.

M i ll ll.

(I fff 0 H LIL- Polyamide imide resins are generally known as thermally stable polymers, and any polyamide imide, which form a tough film can be used preferably in the present invention. The present invention is. therefore not limited to the polyamide imides exemplified above. However, those polyamide imides which have desirable EXAMPLE 1 'y-Fe 0 fine powders 300 parts by weight graphite Pyrodic I00" (polyamide imide resin of Dainippon Ink and Chemicals, Incorporated) 400 dimethyl acetamide 600 The composition of the foregoing formulation was treated in a ball mill, and the polyamide imide resin was dissolved and y-Fe o fine powder and graphite was uniformly dispersed in the resin solution. The resulting 40 dispersion was uniformly coated on a film of the same polyamide imide resin as above containing a primer layer of 0.2 ,1. thick, in a dry thickness of 10 u, and

dried at 180C. The coated product was cut into tape form to produce magnetic recording tapes.

The tape was mounted in a tape recorder, and caused to run for 3 minutes at 400C. and then continuously for 25 hours at 200C. The tape retained their properties.

For comparison, a magnetic recording tape was proproperties as a binder for the present invention have a dllced using a P y y terephthalam mm as 3 molecularweight ranging from 10,000 to 60,000.

As the solvent for dissolving the polyamide imide, therecan be used polar solvents, such as dimethyl acetamide or N-methylpyrrolidone.-

The production of the magnetic recording material of the invention usingthese materials can be performed in quite the same way as in the case of using the conventional binders.

Ferromagnetic fine powders used for the production of the magnetic recording materials of this invention are fine powders of 'y-Fe O Fe O Co-containing 'y-Fe o Co-containing Fe O zn Fe QFeo port and a polyurethane resin as a binder. The running EXAMPLE 2 Example 1 was repeated except that a composition of the following formulation was used instead of the composition used in Example 1.

300 parts by weight resin produced by Dainippon Ink dimethyl fomiamide As a comparative sample, a magnetic recording tape was produced using a vinyl chloride/vinylacetate copolymer as a binder. This magnetic recording tape was useless because the magnetic layer was considerably 1 softened.

EXAMPLES Example 1 was repeated except that a composition of the following formulation was used instead of the composition of Example 1.

Fe-co Ni alloy fine powder 300 parts by weight Silicone oil 5 Polyamide imide resin 100 Graphite fine powders 20 Dimethyl acetamide 600 This composition wascoated on an aluminum substrate plate by the spin coating method, to produce a magnetic disc. The magnetic disc was subjected to a heat-resistant test in an electric oven at 200C., but no change was observed onthe surface of the disc. When a high load was exerted on the magnetic head and the magnetic layer surface of the disc was rubbed, the wear of the surface was 0.2 p at the end of 100 hour period.

5 The magnetic recording tape so obtained was sub- EXAMPLE 4 jected to a running test for 28 consecutive hours at K g I 7 200C. and it was found that it sufficiently retained 7 5-4 3 300 P y weight 7 properties as a magnetic recording material, and i g proved very tough against frictional injury owing to the 5 1 Polyamide imide resin 150 ag ti h d Dimethyl acetamide 400 i Dimethyl formamide 150 The above composition was treated in a ball mill to form a coating solution. The coating solution was applied on a high tensile. strength glass cloth, and dried at '250C. for 30 minutes. The product was then heattreated at 280C. for'30 minutes, and then slit into a width of 1 inch to form a magnetic belt. The magnetic belt-obtained was subjected to a durability test inan electric oven at 230C, and it was found that at the end of 48 hours, it did not show any change.

Althoughthe present invention has-been adequately discussed in the foregoing specification and examples included therein, it is readily apparent that various changes and modifications can be made without cleparting from the spirit and scope thereof.

What is claimed is:

l. A magnetic recording material comprising:

a. a support and 1 .b. a magnetic layer composed of a'finely divided powder of a ferromagnetic material dispersed in a polyamide imide resin binder, I

wherein said polyamide imide resin has the following repeating structural unit: 

